Sintered alloy having wear resistance at high temperature

ABSTRACT

The present invention relates to sintered alloys having wear resistance at high temperature composed of a copper-base alloy containing copper as a principal constituent and 4 to 15 percent of tin, 4 to 25 percent of nickel, and 4 to 25 percent of chromium.

Elnited @tates ?atent [1 1 Niimi et a1.

SINTERED ALLOY HAVING WEAR RESISTANCE AT HIGH TEMPERATURE Inventors: Itaru Niimi, Nagoya; Kametaro Hashimoto, Toyota; Kenzi Ushitani, Toyota; Yoichi Serino, Toyota; K0 Ishihara, Toyota; Seishu Mitani, Kyoto; Kunizo Imanishi, Nagoya, all of Japan Assignee: Toyota Jidosha Kogyo Kabushiki Kaisha, Toyota City, Japan Filed: Oct. 4, 1971 Appl. No.: 186,424

Foreign Application Priority Data '1 1 Feb. 5, 1974 9 [56] References Cited UNITED STATES PATENTS 2,753,859 7/1956 Bartlett 29/1821 X 2,849,789 9/1958 Thomson 2,887,765 5/l959 Thomson et al.

2,983,996 5/1961 Neely et al 29/182 Primary Examiner-Carl D. Quarforth Assistant Examiner-R. E. Schafer Attorney, Agent, or Firm-Arthur G. Connolly; Rudolf E. Hutz et al.

[5 7] ABSTRACT The present invention relates to sintered alloys having wear resistance at high temperature composed of a copper-base alloy containing copper as a principal constituent and 4 to 15 percent of tin, 4 to 25 percent of nickel, and 4 to 25 percent of chromium.

.. Elaine. NqPrawi tas SINTERED ALLOY HAVING WEAR RESISTANCE AT HIGH TEMPERATURE BACKGROUND OF THE INVENTION The present invention relates to copper-base sintered alloys having wear resistance and corrosion resistance at high temperature. These alloys are most suitable as construction materials for internal combustion engines, particularly the valving components of the engine.

Lead is commonly used as an additive for gasoline used in running internal combustion engines. As is well known, the lead additive prevents engine knock. The lead additive also has a lubricating effect which is produced by the adhesion of the lead onto the surface of the valves or valve seat. On the other hand, Ieadfree gasoline and liquid propane gas (LPG) have been used as fuel in response to corrective measures to the airpollution problem. However, the use of such leadfree fuels results in a loss of the lubricating effect attributable to the lead and causes wear of conventional valving materials like cast iron or heat resistant steel. Eventually, the output of the engine is lowered.

The present invention eliminates the abovementioned defects by providing sintered alloys having excellent wear resistance and corrosion resistance at high temperature.

SUMMARY OF THE INVENTION copper as a principal constituent, 4 to percent tin,-

4 to 25 percent nickel, and 4 to 25 percent chromium.

DETAILED DESCRIPTION OF THE INVENTION The sintered alloys according to the present invention are alloys containing chromium dispersed in copper-tin-nickel matrixes, namely copper-base sintered alloys composed of copper as a principal constituent, 4 to 15 percent tin, 4 to 25 percent nickel, and 4 to 25 percent chromium. The density is more than 88 percent of the theoretical one.

Since the sintered alloys of the present invention have remarkable wear resistance and corrosion resistance at high temperature, these alloys are most suitable for valve seats of internal combustion engines in which leadfree gasoline or LPG is used as fuel. The alloys are also applicable as bearing materials, especially for bearings subjected to high temperatures, such as, bearings for hot rollers.

The following description explains the function of each constituent element and the reason for restricting the composition range of the alloys. It is noted that percentages of the elements are all shown by weight.

Among the constituents of the sintered alloys of the present invention, copper excels in heat conductibility and corrosion resistance. It is remarkable that this constituent forms a copper oxide in conjunction with oxygen at high temperatures which imparts a lubricating effect thereby contributing to the wear resistance.

Tin, as in the case of copper, forms a film oxide at high temperature thereby contributing to the wear resistance. It also advances the mechanical strength.

However, such effect is little observed at less than 4 percent, and at more than 15 percent the mechanical strength sharply drops as well as the ability of holding chromium. Therefore, the range is determined as 4 to 15 percent for tin.

Nickel possesses a heat resistance and a corrosion resistance. It permeates into copper in the form of a solid solution thereby strengthening the matrix. However, less than 4 percent nickel has little effect, and more than 25 percent does not cause a remarkable effect considering the quantity added. Hence, the nickel composition is preferably 4 to 25 percent.

Chromium does not reduce in hardness even at high temperature. Also it forms a chromium oxide together with oxygen at high temperature thereby increasing the wear resistance. However, such effect is slight at less than 4 percent. With up to 35 percent chromium the wear resistance advances in proportion to the quantity added, but the mechanical strength diminishes. Therefore, the preferred maximum is 25 percent.

Concerning the density of the alloy, when it is somewhat less than 88 percent of the theoretical one within the above-mentioned range of the constituents, the radiation at high temperature deteriorates and permanent strain of the engine structures results quite soon after engine start-up. This seriously affects the lifetime of the engine. Therefore, the density of the alloys should be more than 88 percent.

As described above, the sintered alloys of the present invention contain chromium which is hard and has excellent wear resistance at high temperature. The chromium is dispersed in massive form into copper-tinnickel matrixes which are comparatively mild and have a good heat conductibility, wear resistance and corrosion resistance as well as a suitable material strength. Thus, these alloys consist of both the phase of hardness and that of mildness and have an excellent wear resistance particularly at high temperature. Furthermore, by providing the alloys with increased density, the heat conductibility is increased at high temperature and under heavy load thereby contributing to prevention of permanent strain.

It is further noted that the sintered alloys according to the present invention have the advantage of being simplified in their constituent materials and production method thereby maintaining easily a stable quality in mass production. The present invention is described as follows.

EXAMPLE 1 utes in a neutral gas atmosphere, and the resultant sintered mass is again pressed under a pressure of 7 t/cm thereby increasing the density up to 7.6 g/cm. A sintered alloy according to the present invention is obtained.

EXAMPLE 2 After the same powders as in Example 1 are arranged and mixed so as to give copper 74.8 percent, nickel 8.8 percent, tin 4.4 percent and chromium 12 percent, the mixture is formed under a forming pressure of 5 t/cm into a formed mass having a density of 7.5 g/cm. Then,,the formed mass is sintered'at 860C. for 60 minutes in a neutral gas atmosphere. The resulting sintered mass is again pressed to increase the density up to 8.1 g/cm. A sintered alloy of the present invention is obtained.

The following table shows, along with those of the conventional materials, the results of the tests made relating to the characteristics and the quantities of wears at high temperature of the alloys of the present invention as obtained in Examples 1 and 2.

TABLE Type of Composition Stensile Hardness Quantities of alloy of Strength Hv(0.2) wear (mm) Constituents (kg/(2m (7: by weight) Alloys of the Present Invention Example 1 56Cu-20Ni-4Sn-20Cr 400-450(Cr 0137 24 in the massive form) 120-140 '(matrix) Comparison of Examples Special Cast Fe-3i5C-25Si-lMn-O.5P-0.SCr-0.5Mo-0.1V 7.42

Iron 40 250-300 Heat Fe-0.4C-2Si-lSCr-ISNi-ZW OQMII 6188 Resistant 2903 10 Steel In the above table, the quantities of wear are indicated by the worn away quantities in millimeters in the direction of height of the specimens measured after the testing continued for a fixed duration hours) by the so-called sliding high-cycle impact tester. This tester has a mechanism wherein 2,500 shocks a minute are given under a surface pressure of 30 kg/cm by means ofajig made of heat resistant steel while the angular specimens fixed to cast iron by special means are rotated 10 times a minute at an elevated temperature of 500 to 550C.

What is claimed is:

1. A sintered copper based alloy compact having wear resistance at high temperature consisting essentially of 4 to 15 percent tin, 4 to 25 percent nickel, 4 to 25 percent chromium. the balance being copper, the alloy having a density greater than 88 percent of the theoretical density.

2. A valve seat for an internal combustion engin comprising a sintered alloy as in claim 1. 

2. A valve seat for an internal combustion engine comprising a sintered alloy as in claim
 1. 